The temporomandibular joint (TMJ) is a complex synovial joint essential for mastication, speech, and jaw movement. TMJ disorders (TMDs) include a spectrum of conditions such as internal derangements, degenerative arthritis, inflammatory disease, and trauma. Imaging plays a vital role in diagnosis, staging, and treatment planning.
📌 Imaging Modalities in TMJ Disorders
1. Plain Radiographs
- Rarely used now but can show:
- Gross osseous changes.
- Fractures of the mandibular condyle.
- Limited role due to poor soft tissue resolution.
2. Orthopantomogram (OPG)
- Initial screening tool.
- Detects condylar morphology, asymmetry, erosions, remodeling.
3. CT (Computed Tomography)
- Best for bone detail.
- Indications:
- Fractures of condyle.
- Ankylosis evaluation.
- Advanced osteoarthritis changes (erosions, osteophytes, sclerosis).
4. MRI (Gold Standard for TMJ Disorders)
- Excellent for soft tissue, disc, and joint space.
- Key findings:
- Disc position:
- Normal = biconcave disc between condyle and fossa.
- Displacement (anterior/posterior/lateral).
- Disc morphology: flattening, perforation, deformation.
- Joint effusion: high signal on T2.
- Articular cartilage and marrow edema.
- Disc position:
- Dynamic/functional MRI assesses disc-condyle relationship during opening/closing.
5. Ultrasound (US)
- Non-invasive, real-time.
- Useful for detecting joint effusion, gross disc displacement.
- Limited by operator dependency.
📍 Common TMJ Disorders on Imaging
- Internal Derangement
- Disc displacement (with/without reduction).
- MRI: anterior disc displacement = most common.
- Degenerative Joint Disease (Osteoarthritis)
- CT: erosion, sclerosis, osteophytes, flattening.
- MRI: cartilage loss, marrow changes, disc degeneration.
- Inflammatory Arthropathies (RA, PsA, JIA)
- MRI: pannus formation, erosions, synovitis, effusion.
- US: synovial thickening, Doppler hypervascularity.
- Trauma
- CT: condylar fractures, dislocation.
- MRI: associated disc injury or hemarthrosis.
- TMJ Ankylosis
- CT: bony fusion across joint space.
- MRI: associated soft tissue involvement.
⚡ Teaching Pearls
- MRI is the modality of choice for internal derangements and soft tissue changes.
- CT is superior for fractures, ankylosis, and advanced bony pathology.
- Dynamic MRI adds value in assessing functional disc-condyle relationships.
🆚 CT vs MRI in TMJ Disorders
| Feature | CT (Computed Tomography) | MRI (Magnetic Resonance Imaging) |
|---|---|---|
| Best for | Osseous detail | Soft tissue & disc assessment |
| Disc position | Not visualized | Clearly seen (anterior, posterior, lateral displacement) |
| Disc morphology | Not visualized | Flattening, perforation, degeneration |
| Joint space | Indirectly assessed (bony changes) | Direct assessment, effusion detection |
| Cartilage | Cannot be assessed | Evaluates articular cartilage integrity |
| Bone changes | Excellent (erosions, osteophytes, sclerosis, ankylosis, fractures) | Seen indirectly, less sensitive than CT |
| Joint effusion | Not detected | Hyperintense on T2, well detected |
| Inflammatory changes | Limited | Excellent (pannus, synovitis, marrow edema) |
| Dynamic assessment | Not possible | Cine/dynamic MRI shows disc-condyle relationship during motion |
| Radiation | Yes | No |
✅ Key takeaway:
- CT = bone (fracture, ankylosis, arthritis).
- MRI = disc + soft tissue + function.
